1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup apparatus which is equipped with the zoom lens system.
2. Description of the Prior Art
It is required for a zoom photographic optical system and a zoom finder optical system of a silver salt camera and a digital camera to have a compact design and a high vari-focal ratio. These two requirements are contrary to each other and must be balanced in a high dimension in particular.
Used conventionally as zoom photographic optical systems are a zoom lens system which is configured as a collapsible mount type so as to have a short total length at a portative time and a zoom lens system which is composed of two positive lens unit and negative lens unit or three positive lens unit, positive lens unit and negative lens unit so as to have a short total length at a wide position and a tele position.
However, the zoom lens system including the collapsible mount type moves a lens unit (zooming lens unit) for a long distance for zooming, thereby having defects that the lens system not only has a large total length but also complicates a lens barrel structure and enlarges a camera as a whole.
Furthermore, the lens system finally has a large total length to reserve a distance for moving the zooming lens unit. In order to shorten a moving distance of the zooming lens unit reversely and enhance a vari-focal ratio, a focusing mechanism or the like requires remarkably delicate precision, thereby enlarging influences on a cost, performance and so on.
Furthermore, there is known a zoom photographic optical system which is configured to reduce a number of lens units to be moved for zooming and the like using a refractive power variable optical element and share an image surface correcting function with this optical element.
This refractive power variable optical element is an element which changes a refractive index of a liquid crystal or an element which changes a shape. As concrete examples of this refractive power variable optical element, there are known elements disclosed by Japanese Patent Kokai Publications No. Hei 7-151908 and No. 7-49404. These elements are elements which change refractive power by changing shapes of lenses with ressures or the like. Furthermore, known as other refractive power variable optical elements are elements disclosed by Japanese Patent Kokai Publications No. Hei 10-48597 and No. Hei 10-73758. These elements are elements using a liquid crystal or the like which changes a refractive index of a medium with an electrical function and application of the elements to optical systems are described in the publications.
As conventional examples in which focusing functions of photographic optical systems are shared using these refractive power variable optical elements, there are known optical system disclosed by Japanese Patent Kokai Publications No. Sho 60-254014 and No. Sho 63-179309. These optical systems are configured to correct changes of image surfaces caused by zooming with refractive power variable optical elements such as those described above.
As a conventional example of zoom photographic optical system which uses a refractive power variable optical element, an optical system disclosed by Japanese Patent Kokai Publication No. Sho 63-208818 uses a refractive power variable optical element, thereby performing zooming without changing airspaces between a plurality of zooming lens units.
Furthermore, an optical system disclosed by Japanese Patent Kokai Publication No. Sho 61-284719 is known as an optical system which performs focusing using a refractive power variable optical element.
The above described conventional examples of optical system using the refractive power variable optical elements have a defect that changes of refractive power of the optical elements themselves is small.
Furthermore, the above described conventional examples are insufficient as optical systems which are compact and have high vari focal ratios.
An object of the present invention is to provide a zoom lens system comprising at least two lens units and configured to change a magnification by moving the lens units in different loci, wherein a refractive power variable optical element is disposed in each lens unit.
Another object of the present invention is to provide a zoom lens system comprising at least two lens units and configured to change a magnification from a wide position to a tele position by moving the lens units so as to have different loci, wherein at least one lens unit out of the lens units has a refractive power variable optical element and the lens unit satisfies the following condition (1):
xe2x80x83xcfx86V(T) less than xcfx86V(W)xe2x80x83xe2x80x83(1)
Furthermore, another object of the present invention is to provide a zoom lens system comprising at least two lens units and configured to change a magnification from a wide position to a tele position by moving the respective lens units in different loci, wherein at least a lens unit out of moving lens units has an optical element variable in a front principal point location, the zoom lens system has a lens unit disposed on the object side of the lens unit which has the optical element and satisfies the following condition (2):
(DF(W)xe2x88x92DF(T))/(HF(W)xe2x88x92HF(T)) greater than 0xe2x80x83xe2x80x83(2)
Furthermore, still another object of the present invention is to provide a zoom lens system comprising at least a focusing lens unit which is moved for focusing out of lens units, using at least one refractive power variable optical element in the focusing lens unit or a lens unit located on the object side of the focusing lens unit and having a negative product of (xcex2R(W)xe2x88x92xcex2R(T)) multiplied by (xcfx86V(W)xe2x88x92xcfx86V(T)), that is, satisfying the following condition (4):
(xcex2R(W)xe2x88x92xcex2R(T))(xcfx86V(W)xe2x88x92xcfx86V(T)) less than 0xe2x80x83xe2x80x83(4)
Further another object of the present invention is to provide a zoom lens system comprising at least two lens units and configured to change a magnification from wide position to a tele position by moving these lens units in different loci respectively, characterized in that at least a lens unit of the above described lens units has an optical element variable in a rear principal point location, and that the zoom lens system has another lens unit on the image side of the lens unit having the optical element variable in the rear principal point and satisfies the following condition (3):
(DR(W)xe2x88x92DR(T))/(HR(W)xe2x88x92HR(T)) less than 0xe2x80x83xe2x80x83(3)